Photopolymerization of dendritic methacrylated polyesters. I. Synthesis and properties

The so-termed starburst dendritic polyesters differ from classical polymers by their structural symmetry, high degree of branching, and high density of terminal functionality. The divergent synthesis of a series of polydisperse dendritic polyesters based upon pentaerythritol and 1,2,4-benzenetricarboxylic anhydride, modified by glycidvl methacrylate and methacrylic anhydride, is described, proceeding in a stepwise growth manner starting from an “initiator core,” building branched arms. These materials have about eight (two samples), 12, or 16 methacrylate double bonds (indicated as D-1-OH, D-1, D-2, and D-3, respectively) at the chain extremities on each molecule. The rheological behavior was investigated by measuring the dynamic viscosity of the dendritic polyesters. The viscosities of the dendritic polyesters largely decrease in the order D-1-OH, D-1, D-2, and D-3 at lower frequency, but the viscosities of D-1-OH and D-1 decrease dramatically at higher frequency. Using a viscometric cup, the flow time of the dendritic methacrylated polyesters was compared with epoxy acrylate-modified unsaturated polyester of a linear type and it was shown that the flow time for the former is only one-third of that for the latter. The thermal mechanical properties and glass transition temperatures of the UV-cured films increase with the degree of terminal functionality. © 1996 John Wiley & Sons, Inc.